The mailbox rule applies when a party seeks judicial review of a Workers' Compensation Commission decision in circuit court per Section 19(f)(1) of the Workers' Compensation Act. Under that Section, a proceeding for judicial review must be "commenced" within 20 days after claimant's attorney received the Commission's decision. A proceeding is "commenced" when the request for summons is placed in the mail, consistent with Illinois law which already applies at the first and third stages of the workers' compensation review process: when appealing circuit court decision to appellate court, and when seeking review of arbitrator's decision before the Commission. (KILBRIDE, GARMAN, KARMEIER, and THEIS, concurring.)